Flexible containers consisting of plastic, particularly collapsible tubes for substances such as pastes, jellies, emulsions, liquids, foams, powders, etc., have been heretofore produced by injection molding, extrusion or blowing of plastic to the desired shape. Such techniques, however, have the disadvantage that when using materials best suited for injection molding and which are flexible in polymerized condition, such as for example polyethylene, PVC, PVDC, there are obtained container walls which are rather well permeable to gas. Consequently, the substances filled into the thus produced containers tend to alter after prolonged storage (oxidation, loss of water or other low boiling solvent or ingredient, etc.), and thus, will become useless.
Another significant drawback of these manufacturing techniques for collapsible tubes resides in the actual heading of the tube, that is, the provision of the tube with a closure portion or end. Tubes formed by such methods are not sufficiently formed as to shape and dimension that they can be readily introduced, as such, into a mold cavity for applying the tube cap or head. Consequently, these techniques need specially designed and sealed molds.
The problems of these tubes have been addressed and to a large extent solved by U.S. Pat. No. 3,660,194. Said patent describes a method for the production of fluid-tight collapsible tubes provided with a tube heading. Said method comprises the steps of coating an impervious, substantially strip-shaped carrier foil on at least one side with heat-sealable plastic, forming the coated carrier foil to the shape of the container body by overlapping and heat-sealing adjacent edges of the coated carrier foil, and applying a plastic sheathing over the heat-sealed container body to cover the outside of the container body such that the shape and dimension of the outside surface of the sheathed container body substantially correspond to the shape and dimension of an inner wall of an outer mold part of a tube heading mold, then sealingly inserting an open end portion of the sheathed container body into the mold cavity of the tube heading mold, and with the inner wall of the open end portion of the container body being spaced from an inside wall of an inner mold part, such that by introducing moldable plastic material into the mold cavity said material is formed into the tube heading and brought into contact with the open end portion of the container body, thereby applying substantially radially directed forces to the spaced inner wall of the container body to further urge the outside surface of said end portion of the container body against the inner wall of the outer mold part to thereby prevent escape of moldable plastic material out of the mold cavity, and resulting in a tight connection between the tube heading and the tube body.
Although the method described in U.S. Pat. No. 3,660,194 solves a lot of the problems encountered with other tubes, said method so far was limited to flexible plastics. Since such flexible plastic materials are not compatible with all desired filling substances, there exists a substantial risk that the filled-in substances, due to their contact with the container wall, are subject to chemical reactions or changes, or to alterations in taste or smell, or to changes of consistency, which alterations or changes may reduce their life-time and/or even prevent their intended use. Or the flexible tube materials may be damaged by aggressive filling substances leading to e.g. delamination of laminate.
Thus, there is still a need for a broader variety of collapsible containers, preferably gas-tight and liquid-tight collapsible containers, especially collapsible tubes.